COMMUTER LTT TURNS WRONG DIRECTION ON TAXI OUT.

Narrative

AFTER WE PROCEEDED TO SPOT 2 ON THE GND OF BWI ARPT; GND CALLED US TO HOLD ON THE SPOT; GIVE WAY TO 737; TAXI RWY 15L; A; J; (I THINK). I WAS CONFUSED WHEN HE SAID RWY 15L SINCE ATIS INFO WAS -X 5 OVCST 1 - RF 60/60 CALM 29.81 29.81 33L/R I SHOULD HAVE NOT ACCEPTED THE CLRNC SINCE I DID NOT FULLY UNDERSTAND THE CLRNC. THE CAPT; SO I THOUGHT; UNDERSTOOD IT. I WAS GOING TO VERIFY THE CLRNC BUT THE FREQ BECAME CONGESTED. WE ACTUALLY TAXIED A; B; S; J INTO ILS CRITICAL AREA. GND TOLD A DASH 8 HE WOULD FOLLOW US. THERE WERE 2 DASH 8'S. 1 DASH 8 WAS HOLDING SHORT OF B ON S; THE OTHER HOLDING SHORT OF S ON J. WE FELT THE ONLY WAY A DASH WOULD FOLLOW US IS IF WE TURNED R ON B THEN L ON X. WHILE I WAS MAKING PA WHEN TWR TOLD CAPT WE TAXIED THE WRONG WAY; AND WE WERE IN ILS CRITICAL AREA! HE SAID; HOWEVER; IT WAS NOT GOING TO BE A PROB. I SHOULD HAVE WRITTEN THE TAXI CLRNC DOWN; ALSO SHOULD NOT HAVE STARTED TO TAXI UNLESS WE WERE POSITIVE ON THE RTE TO TAKE. I'M NOT SURE WHAT WOULD PREVENT THIS AS IT WAS THE 4TH DAY OF A 4-DAY TRIP. I HAVE NOTICED A MUCH HIGHER A RATE OF MISTAKES MADE ON THE 4TH DAY OF 4-DAY TRIPS. THIS 4-DAY TRIP HAS DUTY TIMES OF ALMOST 9.5 HRS; 13 HRS; 10.8 HRS AND 9 HRS ON LAST DAY. THE ONLY OTHER THING WOULD HAVE BEEN TO STOP AND WAIT UNTIL WE COULD VERIFY THE CLRNC.